gnulib-tool: Avoid known warnings that reflect Gnulib's coding style.

* m4/gnulib-common.m4 (gl_CC_GNULIB_WARNINGS): New macro.
* gnulib-tool (func_emit_lib_Makefile_am): Add the
GL_CFLAG_GNULIB_WARNINGS to the CFLAGS of all the compilation units of
the library.
(func_emit_tests_Makefile_am): Add the GL_CFLAG_GNULIB_WARNINGS to the
CFLAGS.
(func_import): Emit an invocation of gl_CC_GNULIB_WARNINGS.

1 files changed, 65 insertions, 1 deletions

diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4
index 87a9a751b6..179aac7aa1 100644
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -1,4 +1,4 @@
-# gnulib-common.m4 serial 69
+# gnulib-common.m4 serial 70
 dnl Copyright (C) 2007-2022 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -879,6 +879,70 @@ AC_DEFUN([gl_CXX_ALLOW_WARNINGS],
   AC_SUBST([GL_CXXFLAG_ALLOW_WARNINGS])
 ])
 
+# gl_CC_GNULIB_WARNINGS
+# sets and substitutes a variable GL_CFLAG_GNULIB_WARNINGS, to a $(CC) option
+# set that enables or disables warnings as suitable for the Gnulib coding style.
+AC_DEFUN([gl_CC_GNULIB_WARNINGS],
+[
+  AC_REQUIRE([gl_CC_ALLOW_WARNINGS])
+  dnl Assume that the compiler supports -Wno-* options only if it also supports
+  dnl -Wno-error.
+  GL_CFLAG_GNULIB_WARNINGS=''
+  if test -n "$GL_CFLAG_ALLOW_WARNINGS"; then
+    dnl Enable these warning options:
+    dnl
+    dnl                                       GCC             clang
+    dnl -Wno-cast-qual                        >= 3            >= 3.9
+    dnl -Wno-conversion                       >= 3            >= 3.9
+    dnl -Wno-float-conversion                 >= 4.9          >= 3.9
+    dnl -Wno-float-equal                      >= 3            >= 3.9
+    dnl -Wimplicit-fallthrough                >= 3            >= 3.9
+    dnl -Wno-pedantic                         >= 4.8          >= 3.9
+    dnl -Wno-sign-compare                     >= 3            >= 3.9
+    dnl -Wno-sign-conversion                  >= 4.3          >= 3.9
+    dnl -Wno-type-limits                      >= 4.3          >= 3.9
+    dnl -Wno-undef                            >= 3            >= 3.9
+    dnl -Wno-unsuffixed-float-constants       >= 4.5
+    dnl -Wno-unused-function                  >= 3            >= 3.9
+    dnl -Wno-unused-parameter                 >= 3            >= 3.9
+    dnl
+    cat > conftest.c <<\EOF
+      #if __GNUC__ >= 3 || (__clang_major__ + (__clang_minor__ >= 9) > 3)
+      -Wno-cast-qual
+      -Wno-conversion
+      -Wno-float-equal
+      -Wimplicit-fallthrough
+      -Wno-sign-compare
+      -Wno-undef
+      -Wno-unused-function
+      -Wno-unused-parameter
+      #endif
+      #if __GNUC__ + (__GNUC_MINOR__ >= 9) > 4 || (__clang_major__ + (__clang_minor__ >= 9) > 3)
+      -Wno-float-conversion
+      #endif
+      #if __GNUC__ + (__GNUC_MINOR__ >= 8) > 4 || (__clang_major__ + (__clang_minor__ >= 9) > 3)
+      -Wno-pedantic
+      #endif
+      #if __GNUC__ + (__GNUC_MINOR__ >= 3) > 4 || (__clang_major__ + (__clang_minor__ >= 9) > 3)
+      -Wno-sign-conversion
+      -Wno-type-limits
+      #endif
+      #if __GNUC__ + (__GNUC_MINOR__ >= 5) > 4 || (__clang_major__ + (__clang_minor__ >= 9) > 3)
+      -Wno-unsuffixed-float-constants
+      #endif
+EOF
+    gl_command="$CC $CFLAGS $CPPFLAGS -E conftest.c > conftest.out"
+    if AC_TRY_EVAL([gl_command]); then
+      gl_options=`grep -v '#' conftest.out`
+      for word in $gl_options; do
+        GL_CFLAG_GNULIB_WARNINGS="$GL_CFLAG_GNULIB_WARNINGS $word"
+      done
+    fi
+    rm -f conftest.c conftest.out
+  fi
+  AC_SUBST([GL_CFLAG_GNULIB_WARNINGS])
+])
+
 dnl gl_CONDITIONAL_HEADER([foo.h])
 dnl takes a shell variable GL_GENERATE_FOO_H (with value true or false) as input
 dnl and produces